1. Field of the Invention
The present invention relates to reformation of soft tissues within the body. More particularly, the invention relates to compositions useful in reforming the shape of soft tissues and methods of using such compositions in reforming soft tissues.
2. Description of Related Art
The medical community for many years has been attempting to develop materials and techniques to replace tissues with the body. It may be desirable to replace such tissue due to, for example, injury, disease, side effects of medical procedures and surgeries, and the aging process, for example. In addition, some patients may desire to alter their appearance for cosmetic reasons, particularly the contour of visible soft tissues. Much attention has been given to the reformation of soft tissue to locally increase its volume and change its shape.
To this end, numerous replacement materials have been tried, with certain advantages and disadvantages. Silicone has been used for decades, but can displace and harden over time. Plastic and metal implants have also been used. However, implants such as these may not have a “natural” look or feel, especially as the body changes over time.
Since the early 1980's, injectable collagen has been extensively used in various procedures. Injectable collagen is either synthetic or natural, which is derived from reconstituted bovine collagen. Injectable collagen has been used throughout the body tissues. It may be accurately controlled in both placement and amount, and may have a more “natural” look and feel than other tissue substitutes.
The primary drawback of injectable collagen is its resorbable nature. Collagen quickly undergoes proteolytic degradation within the body, resulting in relatively short clinical effectiveness. Patients must receive additional injections to maintain tissue reformation, usually at an interval of about every few months. Continual submission to the injection procedure causes the patient inconvenience, expense, and perhaps pain, discomfort, and other side effects. As with any invasive medical procedure, injection carries with it the risk of cross-contamination and infection. Moreover, as the collagen is resorbed by the body, the patient may suffer a return of the physical dysfunction the injection corrected, or experience undesirable and irregular changes in cosmetic appearance.
More recently, concern has arisen in the medical and veterinary communities regarding the transmission of tissue-born diseases among animal species and humans. For example, bovine spongiform encephalopathy may move from animals to humans and cause new variant Creutzfeld-Jacob disease, which is fatal. Accordingly, some medical experts have searched for synthetic alternatives that reduce the use of animal-based tissues.
U.S. Pat. No. 4,536,158 issued to Bruins and Ashman discloses a synthetic porous implantable bony tissue replacement. A prosthesis is formed by bonding together a material composed of polymeric particles.
U.S. Pat. Nos. 4,535,485 and 4,547,390, issued to Ashman et al., disclose a synthetic material and method for making hard tissue replacement prostheses. That material is comprised of polymeric particles coated with a hydrophilic polymeric material. The particles are of sufficient size to be packed into hard tissue areas of the body, and have pores between the particles of sufficient size for tissue, i.e., hard tissue, to grow into the pores and secure the prostheses.
U.S. Pat. No. 4,728,570 issued to Ashman et al. also discloses a hard tissue prosthesis material. That material comprises polymeric particles coated with a hydrophilic polymeric material, with calcium hydroxide distributed on the surfaces and within the material to induce hard tissue growth into the pores between the particles. The particles may be bonded together to form an implantable prosthesis or may be used as a packing material for forming a hard tissue prosthesis in vivo. The material is sold by Bioplant, Inc. of South Norwalk, Conn., under the trade name Bioplant® HTR®.
In U.S. Pat. Nos. 4,902,511 and 4,912,141 issued to Kronman, an implant for fibrous or cartilaginous tissue is disclosed. A sponge-like implant is formed by polymerizing a hydrophilic polymeric material. The implant is shaped by either polymerizing it in a mold or shaping it by cutting or grinding.
While several tissue substitute materials for bony, cartilaginous, and fibrous tissues exist, it would be desirable to have substitute materials for soft tissues. It would also be desirable to have a soft tissue replacement material that was non-resorbable, supple, flexible, and durable so that a patient would not have to undergo repeated procedures. Also, a replacement material that could be implanted in loose (particulate) form for in vivo integration that did not migrate would be highly desirable.